1. Field of the Invention
The present invention relates to a vehicular lamp having an air ventilation hole formed on a part of a lamp body for communicating a lamp chamber with the ambient air. More particularly, the invention relates to a vehicular lamp formed of resin, and apparatus and method for molding the lamp.
2. Related Art
Generally, a vehicular lamp for an automobile, e.g., is constituted by a reflector, an electric bulb, etc., both housed in a lamp chamber having a lamp body and a front lens. However, if the lamp chamber is sealed, there is a possibility that dew concentration will be generated on a lens surface when humidity is saturated in the lamp chamber, thereby to decrease light intensity irradiating from the lamp. Accordingly, an air ventilation hole has been provided in order to prevent the dew condensation for communicating the lamp chamber with the ambient air. When the vehicular lamp a body of which is formed of resin is molded, a molding section for forming the air ventilation hole is provided on a corresponding portion of a mold die unit for resin molding. By using the mold die with the molding section, an air ventilation hole is formed on the lamp body at the same time when the lamp body is injection molded by resin.
FIG. 11 is a sectional view showing a lamp having an air ventilation hole of the conventional type. FIG. 12A is a sectional view showing the vicinity of the air ventilation hole formed on the body thereof. The lamp includes a lamp body 1B, an electric bulb 3 supported by a bulb socket 2 on the lamp body 1B, and a lens 4 mounted on a front opening 11 of the lamp body 1B. An air ventilation hole 7B is formed on a part of a rear parabolic surface of the lamp body 1B so as to communicate a lamp chamber defined by the lamp body 1B and lens 4 with the outside ambient air. The air ventilation hole 7B is constructed by a boss 71 projecting from the rear surface of the lamp body 1B and a through hole 72 formed in the boss 71. In this case, on a part where the through hole 72 opens to the inner surface of the lamp body 1B, a diameter dimension of which is designed to be very small so as to prevent water from entering from the outside into the lamp chamber therethrough and also to avoid the adverse influence on light reflection when an inner surface of the lamp body 1B is subjected to reflection treatment to perform as a reflector.
FIG. 12B is a sectional view showing a part of a molding apparatus for resin-molding the lamp body 1B having the air ventilation hole 7B. The molding apparatus includes a stationary mold 101 and a movable mold 102 which define a cavity 103 for molding the lamp body 1B. The movable mold 102 is provided with a recessed part 109 for forming the boss 71 and a molding pin 111B disposed therein for providing the through hole 72. The molding pin 111B is designed to be a stepped member and provided with a tip part 112B which is smaller in diameter than a base part thereof so as to form the tip opening of the through hole 72 very small as described above. Further, in this case, as the tip part 112 of the molding pin 111B is brought into close contact with the cavity surface of the stationary mold 101, the tip surface 112Ba is a slightly tapered and concave curved surface along the parabolic surface of the stationary mold 101.
When a lamp body is molded of resin using this molding apparatus, the movable mold 102 moves toward the stationary mold 101 side and the cavity 103 is defined therebetween, and then resin is injected into the cavity 103. At the molding operation, in order to form an air ventilation hole, the tip surface 112Ba of the molding pin 111B is brought into contact with the cavity surface of the stationary mold 101 by pressing. As the molding pin is formed with its tip surface 112Ba tapered, even when slight shifts in positions between the stationary mold 101 and the movable mole 102 are generated, a component of an abutting force therebetween is given to the tip part 112B of the molding pin.
Therefore, as shown by dotted lines in FIG. 12B, a state where the tip part 112B of the molding pin is bent outward along the curved surface of the stationary mold 101 is generated and as a result an air ventilation hole is formed on the molded lamp body in a bent state. Further, the bending force applied to the molding pin on the tip part 112B increases when the abutting force is large thereby causing problems in that the tip part 112B of the molding pin 111B is largely bent, deformed or broken.
In particular, as it is necessary to form the small-diameter molding pin with the length of the tip part 112B longer than that along the bending modulus of the inner surface of the lamp body 1B, i.e., larger than a distance L in FIG. 12B, it is relatively long and the tip part 112B of the molding pin is easy to be bent.
Further, with the molding apparatus, as it is necessary to fabricate the tip surface 112Ba of the molding pin 111B to be a tapered and slightly concave curved surface so as to correspond to the shape of the cavity of the stationary mold 101, the fabrication of the molding pin 111B, i.e., manufacturing of the mold die, is made more difficult.
Still further, the lamp body 1B is formed thicker and of more resin on the peripheral part of the air ventilation hole 7B than the other parts because of integral formation of the boss 71. Accordingly, since on this part the resin surface is cooled first and then the inner part is cooled, an undesirable shrinkage may be occurred on the inner surface of the lamp body due to the reduction of the resin volume. Such a shrinkage is occurred at unexpected portions of the peripheral part of the air ventilation hole 7B. Therefore, the shrinkage is different among products so that the quality of the lamp body and the entire lamp is deteriorated.